Optical encoder module

An optical encoder module is employed to detect light modulated by a moveable member (e.g., code wheel). The optical encoder includes an emitter having a light-emitting element, and a transparent medium encapsulating the light-emitting element. The transparent medium has a convex aspherical external surface shaped so as to focus light received from the light-emitting element into a substantially collimated beam of light using a single refractive interface for illuminating the movable member. The optical encode module also includes a detector facing the emitter for detecting modulated light of the collimated beam transmitted through the movable member.